Water-based ink for ink-jet recording, ink-jet recording method, ink-jet recording apparatus, and ink container

Abstract

To provide a water-based ink for inkjet recording that can improve the optical density (OD value) of a recorded material using water-based ink without increasing the colorant concentration.SOLUTION: A water-based ink for inkjet recording includes a pigment, water, a penetrating agent, and a binder resin. The penetrating agent includes a compound of formula (1). In formula (1), x is 6 or more. The binder resin includes a urethane bond. The content of the binder resin is more than 1.0 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink for ink-jet recording, an ink-jet recording method, an ink-jet recording apparatus, and an ink container. [Background technology]

[0002] To improve fixability, a method is known in which the affinity between the aqueous ink and the recording medium is increased to improve penetration. However, this method has the problem that the aqueous ink penetrates not only into the surface of the recording medium but also deeply into the recording medium, resulting in a low optical density (OD value). Therefore, a method is known in which the colorant concentration is increased to improve the optical density (OD value) of recorded matter using aqueous ink (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-231711 Summary of the Invention [Problem to be solved by the invention]

[0004] However, increasing the colorant concentration increases the cost and reduces the stability of the aqueous ink.

[0005] Therefore, an object of the present invention is to provide a water-based ink for ink-jet recording that can improve the optical density (OD value) of recorded matter using the water-based ink without increasing the colorant concentration. [Means for solving the problem]

[0006] In order to achieve the above object, the water-based ink for ink-jet recording of the present invention comprises: Contains pigment, water, penetrant, and fixing resin; The penetrating agent contains a compound represented by the following formula (1): the fixing resin has a urethane bond, The content of the fixing resin is more than 1.0% by mass. [ka] In formula (1), x is 6 or greater. [Effects of the Invention]

[0007] The aqueous ink for inkjet recording of the present invention contains a pigment, water, a specific penetrant, and a specific fixing resin, and therefore can improve the optical density (OD value) of recorded matter using the aqueous ink without increasing the colorant concentration. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic perspective view showing the configuration of an example of an inkjet recording apparatus of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of the mechanism by which the water-based ink for ink-jet recording of the present invention improves the optical density (OD value) of recorded matter. DETAILED DESCRIPTION OF THE INVENTION

[0009] The water-based ink for ink-jet recording (hereinafter, sometimes referred to as "water-based ink" or "ink") of the present invention will be described. The water-based ink of the present invention contains a pigment, water, a penetrant, and a fixing resin.

[0010] The pigment is not particularly limited and may be, for example, carbon black, inorganic pigments, or organic pigments. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Examples of inorganic pigments include titanium oxide, iron oxide-based inorganic pigments, and carbon black-based inorganic pigments. Examples of organic pigments include azo pigments such as azo lake pigments, insoluble azo pigments, condensed azo pigments, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye lake pigments such as basic dye lake pigments and acid dye lake pigments; nitro pigments (nitroso pigments); and aniline black daylight fluorescent pigments. Other pigments may also be used as long as they are dispersible in an aqueous phase. Specific examples of these pigments include CI Pigment Black 1, 6, and 7; CI Pigment Yellow 1, 2, 3, 12, 13, 14, 15, 16, 17, 55, 74, 78, 150, 151, 154, 180, 185, and 194; CI Pigment Orange 31 and 43; CI Pigment Red 2, 3, 5, 6, 7, 12, 15, 16, 48, 48:1, 53:1, 57, 57:1, 112, 122, 123, 124, 125, 126, 127, 128, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 185, and 186; Examples of pigments suitable for the aqueous ink of the present invention include CI Pigment Violet 19 and 196; CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 16, 22, and 60; CI Pigment Green 7 and 36; and solid solutions of these pigments. The aqueous ink of the present invention may be prepared by dispersing the pigment in water with a dispersant. Examples of the dispersant include, for example, a common polymer dispersant (pigment dispersion resin, resin dispersant), which may be prepared in-house. Furthermore, in the aqueous ink of the present invention, the pigment may be encapsulated in a polymer.

[0011] The method for dispersing the pigment using the pigment dispersing resin may be, for example, to disperse the pigment using a dispersing device. The dispersing device used for dispersing the pigment is not particularly limited as long as it is a general dispersing machine, and examples thereof include a ball mill, a roll mill, and a sand mill (e.g., a high-speed type).

[0012] The pigment may be a self-dispersing pigment. The self-dispersing pigment is, for example, one in which at least one hydrophilic functional group, such as a carbonyl group, a hydroxyl group, a carboxylic acid group, a sulfonic acid group, or a phosphate group, or a salt thereof, is chemically bonded to the pigment particle, either directly or via another group, thereby enabling dispersion in water without the use of a dispersant. The self-dispersing pigment may be one treated by methods described, for example, in JP-A-8-3498, JP-T-2000-513396, JP-T-2008-524400, JP-T-2009-515007, or JP-T-2011-515535. Both inorganic and organic pigments can be used as raw materials for the self-dispersing pigment. Examples of pigments suitable for the treatment include carbon blacks such as "MA8" and "MA100" manufactured by Mitsubishi Chemical Corporation. The self-dispersing pigment may also be a commercially available product. Examples of commercially available products include "CAB-O-JET (registered trademark) 200," "CAB-O-JET (registered trademark) 250C," "CAB-O-JET (registered trademark) 260M," "CAB-O-JET (registered trademark) 270Y," "CAB-O-JET (registered trademark) 300," "CAB-O-JET (registered trademark) 400," "CAB-O-JET (registered trademark) 450C," "CAB-O-JET (registered trademark) 465M," and "CAB-O-JET (registered trademark) 470Y" manufactured by Cabot Corporation; "BONJET (registered trademark) BLACK CW-2" and "BONJET (registered trademark) BLACK CW-3" manufactured by Orient Chemical Industry Co., Ltd.; and "LIOJET (registered trademark) WD BLACK 002C" manufactured by Toyo Ink Mfg. Co., Ltd.

[0013] The pigment may be used alone or in combination of two or more types. The solid content of the pigment in the total amount of the aqueous ink (pigment solid content amount) is not particularly limited and can be determined appropriately. The pigment solid content amount is, for example, 0.1% to 20% by mass, 1% to 10% by mass, or 2% to 8% by mass. The pigment solid content amount is the mass of the pigment only, and does not include the mass of the resin dispersant and the like (i.e., converted into the amount of active ingredients).

[0014] The water may be ion-exchanged water, pure water, or the like. The amount of water to be blended relative to the total amount of the aqueous ink (water ratio) is determined appropriately depending on the desired ink properties, etc. The water ratio may be, for example, the remainder of the other components. The amount of water to be blended is, for example, 50% to 95% by mass, 55% to 90% by mass, or 60% to 80% by mass.

[0015] As described above, the water-based ink of the present invention further contains a penetrant and a fixing resin.

[0016] The penetrating agent includes a compound represented by the following formula (1): [ka]

[0017] In the formula (1), x may be any number greater than or equal to 6, for example, 6 to 20, 6 to 14, or 6 to 8. Furthermore, x may be either a straight chain or a branched chain.

[0018] Examples of the compound represented by formula (1) include diethylene glycol monohexyl ether (DEHE; x=6, linear) and diethylene glycol mono-2-ethylhexyl ether (EHDG; x=8, branched). From the viewpoint of ease of handling, DEHE is preferred as the compound represented by formula (1), but the present invention is not limited thereto. The compound represented by formula (1) has a standard boiling point of 250°C or higher, and therefore is unlikely to volatilize in the atmosphere at room temperature and normal pressure, thereby reducing the generation of VOCs. The compound represented by formula (1) may be, for example, a commercially available product. One type of the penetrating agent may be used alone, or two or more types may be used in combination.

[0019] The amount of the compound represented by formula (1) relative to the total amount of the water-based ink may be, for example, 0.1% by mass to 20% by mass, 2% by mass to 13% by mass, or 6% by mass to 10% by mass.

[0020] The aqueous ink may further contain another penetrant (a penetrant other than the compound represented by formula (1)) to the extent that the effects of the present invention are not impaired. The other penetrant is not particularly limited and may be, for example, a penetrant having a standard boiling point of 250°C or higher, or, as described below, a penetrant having a standard boiling point of 250°C or lower. Examples of the other penetrant include alkylene diols and glycol ether compounds. Examples of the alkylene diol include 1,2-hexanediol, 1,2-heptanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, and 3-methyl-1,5-pentanediol. Examples of the glycol ether compounds include ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol-n-propyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol-n-propyl ether, diethylene glycol-n-butyl ether, triethylene glycol methyl ether, triethylene glycol ethyl ether, triethylene glycol-n-propyl ether, triethylene glycol-n-butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol-n-propyl ether, propylene glycol-n-butyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol-n-propyl ether, dipropylene glycol-n-butyl ether, tripropylene glycol methyl ether, tripropylene glycol ethyl ether, tripropylene glycol-n-propyl ether, and tripropylene glycol-n-butyl ether.

[0021] When the penetrant is a combination of two or more penetrants containing the compound represented by formula (1), the amount of the penetrant relative to the total amount of the aqueous ink can be appropriately selected depending on the purpose, and the amount of the penetrant is, for example, 0.1% by mass to 20% by mass, 2% by mass to 13% by mass, or 6% by mass to 10% by mass.

[0022] The fixing resin is, for example, a resin that fixes the solid content (e.g., pigment, etc.) in the aqueous ink to the surface of a recording medium, thereby improving fixing properties. The fixing resin is not particularly limited as long as it is a resin that has a urethane bond in its molecule. The urethane bond may be in a side chain, but is preferably in the main chain. In other words, the fixing resin can also be called a urethane-based resin. In addition to the urethane bond, the fixing resin may have, for example, an ether bond, an ester bond, a carbonate bond, etc. in the main chain and / or side chain.

[0023] The fixing resin may be, for example, resin particles contained in a resin emulsion. The resin emulsion is, for example, composed of the resin particles and a dispersion medium (e.g., water), and the resin particles are not dissolved in the dispersion medium but are dispersed with a specific particle diameter.

[0024] The glass transition temperature (Tg) of the fixing resin is not particularly limited, but is, for example, 24°C to 90°C, preferably 40°C to 80°C, and more preferably 60°C to 80°C.

[0025] The average particle diameter of the fixing resin is not particularly limited, but is, for example, 5 nm to 500 nm, preferably 20 nm to 300 nm, and more preferably 20 nm to 100 nm. The average particle diameter can be measured as an arithmetic mean diameter using, for example, a dynamic light scattering particle size distribution analyzer "LB-550" manufactured by Horiba, Ltd.

[0026] The fixing resin can be synthesized by, for example, a conventionally known method. Examples of such methods include a prepolymer method in which a polyol and an excess of isocyanate are reacted to first synthesize an isocyanate-terminated prepolymer and then chain extension is performed; a one-shot method in which a polyol, an isocyanate, and a chain extender are simultaneously polymerized; and a solvent method in which polyurethane is synthesized in a solvent and then the solvent is removed. Note that these are merely examples, and the fixing resin is not limited to those synthesized by these methods.

[0027] The fixing resin may be, for example, a commercially available product. Examples of the commercially available product include "Superflex (registered trademark) 870" and "Superflex (registered trademark) 830SH" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., and "Takelac (registered trademark) W-5661" and "Takelac (registered trademark) W-6061" manufactured by Mitsui Chemicals, Inc. One type of fixing resin may be used alone, or two or more types may be used in combination.

[0028] The blending amount of the fixing resin having a urethane bond relative to the total amount of the water-based ink is not particularly limited as long as it exceeds 1.0% by mass, and specifically may be, for example, 1% by mass to 20% by mass, preferably 2% by mass to 14% by mass, and more preferably 5% by mass to 10% by mass.

[0029] The aqueous ink may further contain other fixing resins (fixing resins other than those having urethane bonds) within the scope of not impairing the effects of the present invention. The other fixing resins are not particularly limited, and examples thereof include acrylic acid resins, maleic acid ester resins, vinyl acetate resins, carbonate resins, polycarbonate resins, styrene resins, ethylene resins, polyethylene resins, propylene resins, polypropylene resins, polyurethane resins, and copolymer resins thereof.

[0030] When the fixing resin is a combination of two or more types of fixing resins including the fixing resin having a urethane bond, the amount of the fixing resin relative to the total amount of the water-based ink can be appropriately selected depending on the purpose. The amount of the fixing resin relative to the total amount of the water-based ink is, for example, 1% by mass to 20% by mass, preferably 2% by mass to 14% by mass, and more preferably 5% by mass to 10% by mass.

[0031] The aqueous ink contains a penetrant containing the compound represented by formula (1) and a fixing resin having a urethane bond, thereby enabling the optical density (OD value) of a recorded product using the aqueous ink to be improved without increasing the colorant concentration. The mechanism by which the optical density (OD value) of a recorded product using the aqueous ink can be improved without increasing the colorant concentration is presumed to be as follows. An example of this mechanism is shown in FIG. 2. In a recording medium having a layered structure (e.g., coated paper having a coating layer as shown in FIG. 2), non-polar and water-insoluble low-molecular-weight components tend to penetrate the inner layer (plain paper) of the recording medium. Therefore, as shown in FIGS. 2(A) and 2(B) , after the aqueous ink lands on the coated paper, low-molecular-weight organic solvent components (e.g., a humectant 11 such as triethylene glycol (TEG)) penetrate into the plain paper, leaving other components (e.g., a penetrant, water, glycerin, pigment 12, fixing resin 13, etc.) on the surface of the recording medium (i.e., on the coating layer). Here, when the penetrant remaining on the surface of the recording medium has hydrophilic properties (e.g., when the penetrant is butyl triglycol (BTG) 14), due to its high affinity with water, the components remaining on the surface of the recording medium exist in a dispersed state, as shown in Figure 2(A). In contrast, among ethylene glycol-based penetrants, compounds 15 represented by formula (1), particularly DEHE and EHDG, have alkyl carbon atoms of 6 or 8 and a hydrophobic structure, resulting in high penetration performance. Thus, compounds 15 represented by formula (1) (DEHE and EHDG) have low affinity with water, and therefore exist in an aggregated state with pigment 12 and fixing resin 13 remaining on the surface of the recording medium, as shown in Figure 2(B). Compounds 15 represented by formula (1) (DEHE and EHDG) connect pigment 12 and fixing resin 13, increasing their apparent size, making it easier for pigment 12 to remain on the surface of the recording medium and increasing the optical density (OD value). Furthermore, fixing resins containing urethane bonds promote the formation of a film of aqueous ink on the surface of the recording medium, further increasing the optical density (OD value). However, this mechanism is merely speculation, and the present invention is not limited to this.

[0032] When the blending amount of DEHE is 2% by mass or more and 3% by mass or less, for example, for the purpose of further improving the optical density (OD value), the blending amount of the fixing resin having a urethane bond may be set to 3% by mass or more. In this case, the upper limit of the blending amount of the fixing resin having a urethane bond is, for example, the same as described above.

[0033] The aqueous ink may contain an organic solvent other than the penetrant. The organic solvent is, for example, a wetting agent. The wetting agent may be, for example, an organic solvent having an SP value of 12 to 14 (hereinafter also referred to as a first wetting agent), or an organic solvent having an SP value other than 12 to 14 (hereinafter also referred to as a second wetting agent), but is preferably an organic solvent having an SP value of 12 to 14. The SP value (Solubility Parameter) is a value calculated, for example, by the Fedors method using the following formula, and is expressed in units of (cal / cm 3 ) 1 / 2 is. SP value = (ΣΔei / ΣΔvi) 1 / 2 Δei: Evaporation energy of atoms and atomic groups (cal / mol) Δvi: molar volume (cm 3 / mol)

[0034] Examples of the wetting agent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol; amides such as dimethylformamide and dimethylacetamide; ketones such as acetone; ketoalcohols such as diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyhydric alcohols such as polyalkylene glycols, alkylene glycols, and glycerin; 2-pyrrolidone; N-methyl-2-pyrrolidone; and 1,3-dimethyl-2-imidazolidinone. The polyalkylene glycol is not limited, and examples thereof include polyethylene glycol and polypropylene glycol. The alkylene glycol is not limited, and examples thereof include ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, thiodiglycol, and hexylene glycol. Among these, polyhydric alcohols such as alkylene glycols and glycerin are preferred. The wetting agent may be used alone or in combination of two or more. For example, a commercially available product may be used as the wetting agent.

[0035] Examples of the first wetting agent include triethylene glycol (TEG; SP value=13.6), tripropylene glycol (TPG; SP value=12.1), and polyethylene glycol (PEG; SP value=12.8) having an average molecular weight of 190 to 210.

[0036] The amount of the first wetting agent relative to the total amount of the aqueous ink may be, for example, 0.1% by mass to 20% by mass, preferably 1% by mass to 10% by mass, and more preferably 3% by mass to 7% by mass.

[0037] It is presumed that the first wetting agent can increase the solubility of the compound represented by formula (1) (penetrating agent) in the aqueous ink, although the present invention is not limited to this presumption.

[0038] When the aqueous ink contains the first humectant, the blending amount (mass%) (A) of the compound represented by formula (1) as the penetrant and the blending amount (mass%) (B) of the solid content of the pigment may satisfy, for example, at least one of 0.5≦A / B≦4.0 (hereinafter also referred to as condition X) and 1.5≦A / B≦3.0 (hereinafter also referred to as condition Y). In this case, the blending amount (mass%) (A) of the compound represented by formula (1) as the penetrant and the blending amount (mass%) (B) of the solid content of the pigment may be appropriately adjusted so as to satisfy the above condition (X) and / or the above condition (Y), and are not particularly limited.

[0039] The second humectant may be, for example, glycerin (SP value=20.0), etc. The amount of glycerin to be added relative to the total amount of the aqueous ink can be appropriately selected depending on the purpose.

[0040] When the humectant is a combination of two or more humectants, including at least the first humectant and the second humectant, the amount of the humectant relative to the total amount of the aqueous ink can be appropriately selected depending on the purpose. The amount of the humectant is, for example, 0% to 95% by mass, preferably 1% to 80% by mass, and more preferably 3% to 50% by mass.

[0041] The water-based ink may further contain, for example, a surfactant.

[0042] The surfactant is not particularly limited and can be appropriately selected depending on the purpose, and for example, a commercially available product may be used.Specific examples of the surfactant include silicone surfactants and acetylene surfactants.In particular, since the silicone surfactant does not contain impurities such as ethylene oxide, using the silicone surfactant as the surfactant can further reduce VOC generation.

[0043] Examples of commercially available silicone surfactants include "Silface (registered trademark) SAG002," "Silface (registered trademark) SAG005," and "Silface (registered trademark) SAG503A," all manufactured by Nissin Chemical Industry Co., Ltd.

[0044] Examples of commercially available acetylene surfactants include "Olfine (registered trademark) E1004," "Olfine (registered trademark) E1008," and "Olfine (registered trademark) E1010" manufactured by Nissin Chemical Industry Co., Ltd.; "Surfynol (registered trademark) 440," "Surfynol (registered trademark) 465," and "Surfynol (registered trademark) 485" manufactured by Air Products and Chemicals, Inc.; and "Acetylenol (registered trademark) E40" and "Acetylenol (registered trademark) E100" manufactured by Kawaken Fine Chemicals Co., Ltd.

[0045] The water-based ink may contain other surfactants in addition to or in place of the silicone-based surfactant and the acetylene-based surfactant. Examples of the other surfactants include nonionic surfactants manufactured by Kao Corporation such as the "EMULGEN (registered trademark)" series, "RHEODOL (registered trademark)" series, "EMASOL (registered trademark)" series, "EXCEL (registered trademark)" series, "EMANON (registered trademark)" series, "AMIET (registered trademark)" series, and "AMINON (registered trademark)" series; nonionic surfactants manufactured by Toho Chemical Industry Co., Ltd. such as the "SORBON (registered trademark)" series; nonionic surfactants manufactured by Lion Corporation such as the "DOBANOX (registered trademark)" series, "LEOCOL (registered trademark)" series, "LEOX (registered trademark)" series, "LAOL,LEOCOL (registered trademark)" series, "LIONOL (registered trademark)" series, "CADENAX (registered trademark)" series, "LIONON (registered trademark)" series, and "LEOFAT (registered trademark)" series; and anionic surfactants manufactured by Kao Corporation such as the "EMAL (registered trademark)" series, "LATEMUL (registered trademark)" series, "VENOL (registered trademark)" series, and "NEOPELEX (registered trademark)" series, NS SOAP, KS SOAP, OS SOAP and the "PELEX (registered trademark)" series, etc.; anionic surfactants manufactured by Lion Corporation such as the "LIPOLAN (registered trademark)" series, "LIPON (registered trademark)" series, "SUNNOL (registered trademark)" series, "LIPOTAC (registered trademark) TE, ENAGICOL" series, "LIPAL (registered trademark)" series and "LOTAT (registered trademark)" series; and cationic surfactants manufactured by Daiichi Kogyo Seiyaku Co., Ltd. such as "Catiogen (registered trademark) ES-OW" and "Catiogen (registered trademark) ES-L".

[0046] The surfactants may be used alone or in combination of two or more.

[0047] The amount of the surfactant relative to the total amount of the aqueous ink can be appropriately selected depending on the purpose. The amount of the surfactant is, for example, 0.1% by mass to 5% by mass, preferably 1% by mass to 3.5% by mass, and more preferably 1.5% by mass to 3% by mass. The amount of the surfactant referred to here is the total amount of two or more surfactants.

[0048] The aqueous ink may further contain conventionally known additives as needed. Examples of the additives include a pH adjuster, a viscosity adjuster, a surface tension adjuster, and an anti-mold agent. Examples of the viscosity adjuster include polyvinyl alcohol, cellulose, and a water-soluble resin.

[0049] The aqueous ink may be, for example, an aqueous ink for a recording medium having a layered structure. The layered structure may, for example, have at least two layers with different absorption rates for the aqueous ink. At least one of the layers may be formed, for example, by applying a specific coating. The recording medium having the layered structure is not particularly limited and may, for example, be coated paper, glossy paper, etc. "Coated paper" refers to plain paper, such as high-grade printing paper or medium-grade printing paper, which is primarily made of pulp and to which a coating agent has been applied to improve smoothness, whiteness, gloss, etc., specifically high-grade coated paper, medium-grade coated paper, etc. "Glossy paper" refers to a recording medium including, for example, an image-forming layer that creates a glossy texture, an ink-absorbing layer with high ink absorption, a white background adjustment layer that creates a high-whiteness white color, and a base paper for adjusting thickness.

[0050] The ink container of the present invention is an ink container containing an aqueous ink for ink-jet recording, characterized in that the aqueous ink is the aqueous ink for ink-jet recording of the present invention. Examples of the ink container include an ink cartridge, a tank, a pouch, etc. The main body of the ink container can be, for example, a conventionally known one.

[0051] Next, the ink jet recording apparatus and ink jet recording method of the present invention will be described.

[0052] The inkjet recording apparatus of the present invention includes an ink storage unit and an ink ejection means, and ejects ink stored in the ink storage unit by the ink ejection means, and is characterized in that the ink storage unit stores the water-based ink for inkjet recording of the present invention.

[0053] The configuration of an example of an inkjet recording apparatus of the present invention is shown in Figure 1. As shown in the figure, this inkjet recording apparatus 1 includes, as its main components, four ink storage units (ink cartridges 2), an ink ejection means (inkjet head) 3, a head unit 4, a carriage 5, a drive unit 6, a platen roller 7, and a purge device 8.

[0054] The four ink cartridges 2 contain one each of four colors of water-based ink: yellow, magenta, cyan, and black. For example, at least one of the four colors of water-based ink is the water-based ink of the present invention. In this example, a set of four ink cartridges 2 is shown, but instead, an integrated ink cartridge whose interior is partitioned to form a water-based yellow ink storage section, a water-based magenta ink storage section, a water-based cyan ink storage section, and a water-based black ink storage section may be used. The ink cartridge body may be, for example, a conventionally known one.

[0055] The inkjet head 3 installed in the head unit 4 performs recording on a recording medium (e.g., recording paper) P. Four ink cartridges 2 and the head unit 4 are mounted on the carriage 5. A drive unit 6 moves the carriage 5 back and forth in a linear direction. As the drive unit 6, for example, a conventionally known drive unit can be used (see, for example, Japanese Patent Application Laid-Open No. 2008-246821). A platen roller 7 extends in the direction in which the carriage 5 reciprocates, and is disposed opposite the inkjet head 3.

[0056] The purging device 8 sucks out defective ink containing air bubbles and the like that accumulates inside the inkjet head 3. As the purging device 8, for example, a conventionally known device can be used (for example, see Japanese Patent Application Laid-Open No. 2008-246821).

[0057] A wiper member 20 is disposed adjacent to the purging device 8 on the platen roller 7 side of the purging device 8. The wiper member 20 is formed in a spatula shape and wipes the nozzle formation surface of the inkjet head 3 as the carriage 5 moves. In Figure 1, a cap 18 covers the multiple nozzles of the inkjet head 3, which are returned to the reset position when recording is completed, to prevent the water-based ink from drying.

[0058] In the inkjet recording apparatus 1 of this example, the four ink cartridges 2 are mounted on a single carriage 5 together with the head unit 4. However, the present invention is not limited to this. In the inkjet recording apparatus 1, each of the four ink cartridges 2 may be mounted on a carriage separate from the head unit 4. Alternatively, each of the four ink cartridges 2 may be disposed and fixed within the inkjet recording apparatus 1 without being mounted on the carriage 5. In these embodiments, for example, each of the four ink cartridges 2 and the head unit 4 mounted on the carriage 5 are connected by a tube or the like, and the water-based ink is supplied from each of the four ink cartridges 2 to the head unit 4. In these embodiments, four bottle-shaped ink bottles may be used instead of the four ink cartridges 2. In this case, it is preferable that the ink bottles have an inlet for injecting ink from the outside into the ink bottles.

[0059] Inkjet recording using this inkjet recording apparatus 1 is performed, for example, as follows. First, recording paper P is fed from a paper feed cassette (not shown) provided to the side or below the inkjet recording apparatus 1. The recording paper P is introduced between the inkjet head 3 and the platen roller 7. A predetermined recording is made on the introduced recording paper P using aqueous ink ejected from the inkjet head 3. This ejection may be performed, for example, at a first ejection amount as described above, or may be performed at a second ejection amount when specific conditions are met. After recording, the recording paper P is ejected from the inkjet recording apparatus 1. In FIG. 1, the paper feed mechanism and paper ejection mechanism for the recording paper P are not shown.

[0060] 1 employs a serial inkjet head, but the present invention is not limited to this. The inkjet recording device may employ a line inkjet head or a roll-to-roll system.

[0061] The inkjet recording method of the present invention includes a recording step of ejecting an aqueous ink onto a recording medium by an inkjet method, and is characterized in that the aqueous ink for inkjet recording of the present invention is used as the aqueous ink in the recording step. The inkjet recording method of the present invention can be carried out, for example, using the inkjet recording apparatus of the present invention. The recording includes printing, photographic printing, printing, etc. [Example]

[0062] Next, examples of the present invention will be described together with comparative examples. However, the present invention is not limited or restricted by the following examples and comparative examples.

[0063] (Preparation of Pigment Dispersion A) 20% by weight of pigment (CI Pigment Blue 15:3) and 7% by weight of styrene-acrylic acid copolymer neutralized with sodium hydroxide (acid value 50 mg KOH / g, molecular weight 10,000) were mixed with purified water to a total of 100% by weight and stirred to obtain a mixture. This mixture was placed in a wet sand mill filled with 0.3 mm diameter zirconia beads and dispersed for 6 hours. The zirconia beads were then removed using a separator, and the mixture was filtered through a 3.0 μm pore size cellulose acetate filter to obtain pigment dispersion A. Styrene-acrylic acid copolymer is a water-soluble polymer commonly used as a pigment dispersant.

[0064] (Fixing resin A) Fixing resin A was synthesized by reacting glycols with polyisocyanate. During the synthesis, the acid value of fixing resin A was controlled by adjusting the compounding ratio of each component and functional groups such as carboxyl groups and amino groups. The acid value of fixing resin A was measured according to JIS K2501 and was found to be 48 mgKOH / g.

[0065] (Examples 1 to 11 and Comparative Examples 1 to 5) The components of the aqueous ink composition (Table 1) except for the pigment dispersion were mixed uniformly to obtain an ink solvent. Next, the ink solvent was added to the pigment dispersion and mixed uniformly. The resulting mixture was then filtered through a cellulose acetate membrane filter (pore size 3.00 μm) manufactured by Toyo Roshi Kaisha, Ltd., to obtain the aqueous inks for inkjet recording of Examples 1 to 11 and Comparative Examples 1 to 5 shown in Table 1.

[0066] For the aqueous inks of Examples 1 to 12 and Comparative Examples 1 to 5, (a) optical density (OD value) evaluation was carried out by the following method.

[0067] (a) Optical density (OD value) evaluation Using a digital multifunction printer equipped with an inkjet printer, DCP-J4225N, manufactured by Brother Industries, Ltd., an image was recorded on coated paper ("N Mirror 73 P22 G7B" manufactured by Oji Tack Co., Ltd.) using the aqueous inks of the examples and comparative examples to prepare an evaluation sample. The optical density (OD value) at three points in the evaluation sample was measured using a spectrophotometer, SpectroEye, manufactured by X-Rite (light source: D 50 The average value was calculated and evaluated according to the following evaluation criteria.

[0068] Optical density (OD value) evaluation criteria AA: Optical density (OD value) exceeds 2.4 A: Optical density (OD value) is 1.90 or more and 2.39 or less B: Optical density (OD value) is 1.65 or more and 1.89 or less C: Optical density (OD value) is less than 1.65

[0069] Table 1 shows the compositions and evaluation results of the aqueous inks of Examples 1 to 12 and Comparative Examples 1 to 5.

[0070] [Table 1]

[0071] As shown in Table 1, Examples 1 to 12 had favorable optical density (OD value) evaluation results of "B" or higher. Example 1, which contained the first wetting agent, had a better optical density (OD value) evaluation result than Example 6, which was identical except for containing the second wetting agent. Furthermore, Example 1, which satisfied condition X (0.5≦A / B≦4.0) and contained the first wetting agent, had a better optical density (OD value) evaluation result than Example 9, which was identical except for not satisfying condition X. Examples 10 and 11, which satisfied condition Y (1.5≦A / B≦3.0), had a better optical density (OD value) evaluation result than Example 1, which was identical except for not satisfying condition Y.

[0072] On the other hand, Comparative Example 1, in which the compound represented by formula (1) was not used, had a poor evaluation result for optical density (OD value). Comparative Example 2, in which the blending amount of the fixing resin was 1.0 mass % or less, also had a poor evaluation result for optical density (OD value). Comparative Example 3, in which the fixing resin was not used, also had a poor evaluation result for optical density (OD value). Comparative Example 4, in which the compound in formula (1) where x = 4 was used, also had a poor evaluation result for optical density (OD value). And Comparative Example 5, in which an acrylic resin was used instead of the fixing resin (urethane resin) having a urethane bond, also had a poor evaluation result for optical density (OD value). [Industrial Applicability]

[0073] As described above, the aqueous ink of the present invention can improve the optical density (OD value) of recorded matter using the aqueous ink without increasing the colorant concentration. The aqueous ink of the present invention can be widely used in inkjet recording on various recording media. [Explanation of symbols]

[0074] 1. Inkjet recording device 2 ink cartridges 3. Ink ejection means (inkjet head) 4 Head Unit 5 Carriage 6 Drive Unit 7 Platen roller 8 Purging device

Claims

1. The ink contains a pigment, water, a penetrant, a fixing resin, and an organic solvent having an SP value of 12 to 14, The penetrating agent contains a compound represented by the following formula (1): the fixing resin has a urethane bond, The content of the fixing resin exceeds 1.0% by mass, The water-based ink for ink-jet recording is characterized in that the content of the compound represented by the following formula (1) as the penetrating agent and the content of the pigment satisfy the following condition (X): Condition (X): 0.5≦A / B≦4.0 A: Content of the penetrant (mass%) B: Solid content of the pigment (% by mass) 【Chemistry 1】 In formula (1), x is 6 or greater.

2. 2. The water-based ink for ink-jet recording according to claim 1, wherein the compound represented by formula (1) is diethylene glycol monohexyl ether.

3. 3. The water-based ink for ink-jet recording according to claim 1, wherein the organic solvent is triethylene glycol.

4. 4. The water-based ink for ink-jet recording according to claim 1, wherein the content of the compound represented by Formula (1) as the penetrating agent and the content of the pigment satisfy the following condition (Y): Condition (Y): 1.5≦A / B≦3.0 A: Content of the penetrant (mass%) B: Solid content of the pigment (% by mass)

5. The water-based ink for ink-jet recording according to any one of claims 1 to 4, wherein the content of the fixing resin is 5% by mass or more and 10% by mass or less.

6. The water-based ink for ink-jet recording according to any one of claims 1 to 5, which is a water-based ink for ink-jet recording for use on a recording medium having a layer structure.

7. a recording step of ejecting a water-based ink for ink-jet recording onto a recording medium by an ink-jet method, An inkjet recording method, wherein the water-based ink for inkjet recording according to any one of claims 1 to 6 is used as the water-based ink for inkjet recording in the recording step.

8. 8. The ink jet recording method according to claim 7, wherein the recording medium has a layer structure.

9. an ink container and an ink ejection means; an inkjet recording apparatus in which the ink contained in the ink containing section is discharged by the ink discharge means, An inkjet recording apparatus, wherein the ink reservoir contains the water-based ink for inkjet recording according to any one of claims 1 to 6.

10. An ink container containing a water-based ink for ink-jet recording, wherein the water-based ink for ink-jet recording is the water-based ink for ink-jet recording according to any one of claims 1 to 6.

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